The present invention relates to solvent free, moisture-curable, reactive hot melt adhesive compositions that are solid at room temperature, a method of making the adhesive compositions, a laminate prepared from the adhesive compositions and a method of preparing the laminates. More particularly the invention relates to solvent free, moisture-curable, hot melt adhesive compositions comprising a polyurethane prepolymer and a vinyl chloride based thermoplastic copolymer.
Moisture curable reactive hot melt adhesives are known. Typically, these reactive hot melt adhesives are 100% solids materials which do not contain or require solvents. They are solids at room temperature and liquids when heated to application temperatures. The adhesives are used to prepare laminated structures such as garage doors, architectural panels, truck doors, patio enclosure panels, transit panels, cold storage panels, agricultural panels and the like. The materials used for the panel portion of the laminates include coated and uncoated metals, treated and untreated plastics, fiber reinforced plastics (FRP), vinyl, plywood, particleboard, oriented strandboard (OSB) and foam. The adhesive is required to provide structural performance with high moisture resistance and high bond strength. In general, the adhesive is applied in a molten state as a single component with a roller, spraying, etc.
Both batch and continuous processes can be used to prepare a laminate. In a batch process a stack of adhesive coated panels is assembled. The stack is placed in a press and pressure is applied. The pressure of the press on the stack is not released until adhesive strength has developed which is sufficient to bond all the layers of the laminate tightly together. In a continuous process the adhesive coated panel laminate is continuously passed through a nip roller or other device for applying pressure. In the continuous process the adhesive needs to provide immediate adhesive strength (green strength) after rolling or pressing in order to insure that the various layers of the laminate remain bonded until the adhesive is allowed to continue to cure. Reactive hot melt adhesives having quick green strength are particularly suitable for a continuous process.
A number of reactive hot melt polyurethane adhesive compositions are known. U.S. Pat. No. 3,931077 discloses a composition comprising, a polyurethane prepolymer having a viscosity greater than 300,000 cps at 25xc2x0 C.; a thermoplastic resin of an ethylene-vinylacetate copolymer; and a tackifier. U.S. Pat. No. 4,585,819 teaches the combination of a polyurethane prepolymer, a thermoplastic polyurethane or polyester, and a synthetic resin selected from the group consisting of ketone resins, hydrogenated products of acetophenone condensation resins and mixtures thereof. U.S. Pat. No. 4,775,719 discloses compositions comprising; a prepolymer having a viscosity of less than 300,000 cps at 25xc2x0 C., a thermoplastic ethylene-vinylacetate copolymer or ethylene acrylate copolymer, a tackifier and an antioxidant. These compositions are prepared by blending a polyurethane prepolymer with a melted mixture of a thermoplastic polymer and a tackifier at 150xc2x0 C. U.S. Pat. No. 4,808,255 teaches that compatible blends may be prepared by combining a polyurethane prepolymer made by reacting an isocyanate compound with a polyester polyol, a thermoplastic ethylene-vinyl monomer copolymer and tackifying agent at elevated temperatures sufficient to melt the composition but not harm the components. U.S. Pat. No. 5,021,507 discloses thermoplastic acrylic modified reactive urethane hot melt adhesive compositions in which the acrylic component is prepared by polymerizing acrylic monomers in the presence of polyols. An isocyanate is then added to react with the polyol in situ. U.S. Pat. No. 5,527,616 relates to specific uses of hot melt adhesives. It discloses a laminate for flexible packaging using a polyurethane reactive hot melt adhesive. The polyurethane prepolymer contains a polyester polyol component having 3 to 50 mole % of an aromatic component selected from the group consisting of an aromatic diol and an aromatic dicarboxylic acid. Use of the aromatic component is said to markedly improve adhesion to different polyester films. The patent discloses that from 0 to 10 parts by weight of a thermoplastic copolymer may be blended into the composition. U.S. Pat. No. 5,550,191 discloses a catalyzed polyurethane reactive hot melt comprising; a reactive polyurethane adhesive and from 0.05 to 0.15 wt % 2,2xe2x80x2dimorpholinoethyl ether catalyst. This reference discloses a method of improving the cure speed of the composition by including a thermoplastic ABA block, A-(BA)n-B block or radial A-B-A block; where A=polystyrene, B=a rubbery block and n=2-50. U.S. Pat. No. 5,827,926 moisture-curable hot melt compositions comprising a polyurethane prepolymer and a crystalline polymer. The crystalline polymer must contain at least one crystalline monomer. The claimed crystalline monomers are (meth)acrylate esters of non-tertiary alcohols where the alkyl portion is comprised of 16 or more carbons containing no isocyanate reactive hydrogen.
Other references disclose adhesive compositions containing a mixture of a polyurethane prepolymer and a chlorinated resin. Typically, these compositions are dissolved in solvents. They are not reactive hot melts. U.S. Pat. No. 4,217,254 and U.S. Pat. No. 4,340,682 disclose adhesive compositions in solvents consisting essentially of a recinoleate polyurethane prepolymer and a chlorinated rubber or a chlorinated polyvinyl chloride resin. U.S. Pat. No. 4,740,424 discloses compositions containing a polyurethane prepolymer and a halogenated resin compatible with the prepolymer. Polyols used to prepare the prepolymer are selected from the group consisting of polytetramethylene oxide polyols, polycarbonate polyols, and polysulfide polythiols. The halogenated resins contain from 50 to 70 weight percent halogen.
The present invention relates to solvent free, moisture-curable, reactive hot melt adhesive compositions that are solids at room temperature, methods of preparing the compositions, methods of preparing laminates using the compositions of the invention and laminates prepared using the adhesive compositions. The compositions are comprised of an isocyanate terminated prepolymer and a thermoplastic copolymer which is compatible with the isocyanate prepolymer. The isocyanate prepolymer is the reaction product of an aliphatic polyester polyol or mixture of aliphatic polyester polyols and a polyisocyanate or mixture of polyisocyanates. The thermoplastic copolymer is prepared from vinyl chloride monomers and at least one other monomer capable of copolymerizing with the vinyl chloride. The vinyl chloride monomers make up at least 50% by weight of the thermoplastic copolymer.
The thermoplastic copolymer is free of isocyanate reactive groups and has a weight average molecular weight (MW) greater than about 30,000. The vinyl chloride based thermoplastic used in the present invention can decompose releasing hydrogen chloride, during processing and weathering. In order to ensure the effectiveness of the present hot melt compositions a stabilizer can be added. The stabilizer acts as an acid scavenger. Epoxy containing compositions are generally suitable as stabilizers in the compositions of the present invention. Examples of such compositions include epoxidized oils and resins. Many of these compositions also act as plasticizers. In addition, the composition may also contain components typically found in solvent free, moisture-curable, hot melt adhesives such as; catalysts, fillers, antioxidants, adhesion promoters, tackifiers, plasticizers, waxes and the like. The solvent free, moisture-curable, hot melt adhesive compositions of the present invention may be prepared by conventional means, however the compositions of the present invention can also be prepared by a one-step, in-situ process which can be run at moderate temperatures. The use of moderate processing temperatures aids in maintaining the integrity of the adhesive components. One object of the invention is to provide solvent free, moisture-curable, hot melt adhesive compositions which exhibit shear thinning rheological behavior, improved green strength, water resistance, and adhesion to various substrates such as metals, wood, plastics, and foams. Another object of the invention is to provide a simple one step method of preparing the adhesive compositions of the invention. Other objects of the invention include laminates prepared using the claimed adhesive compositions and method of preparing the laminates using the claimed adhesive compositions.
FIG. 1 - viscosity curves for examples 1, 2, 3, and 4.